Syringe push rod



April 29, 1958 M. DANN ETAL SYRINGE PUSH ROD 2 Sheets-Sheet 1 Filed March 26, 1957 WIIIIIM INVENTORS Horns flarm/ .fa/m I fe'fzrsofl Ma C JWTTQRNEY April 29, 1958 M. DANN ETAL smmca PUSH ROD 2 Sheets-Sheet 2 Filed March 26, 1957 :ii A, Wig...

INVENTORS Harris fla 14w filwj Pike/50m AME. I JML E SYRINGE PUSH ROD Morris Dann, Havertown, and John J. I'eterson, Philadelphia, Pa., assignors to American Home Products Corporation, New York, N. Y., a corporation of Delaware Application March 26, 1957, Serial No. 648,655 Claims. (Cl. 128-218) This invention relates to a syringe push rod. More particularly it relates to a push rod especially adapted for use in a disposable injection syringe, the rod having a central bore permitting its use as a needle shield prior to injection, having at its proximal end means for remcvably securing it to a syringe when serving as a needle shield, and having at its distal end means for positive engagement with the syringe plunger when being used for injection, said latter means being afiixed in the distal end of the bore of the push rod by a flexible web, elastic membrane or diaphragm.

In using disposable injection syringes, for example of the type disclosed in Dann Patent 2,671,449, the user removes the push-rod-shield from its position surrounding the needle and attaches its distal end to the syringe plunger by means of the threaded stud on the plunger. At the start of the injection when the syringe is filled with injectable material, the push rod has a relatively short bearing on the interior surface of the syringe and accordingly the push rod may inadvertently be thrown out of axial alinement by the user. With prior push rods rigidly attached to the plunger, this will result in a cocking of the plunger. Because of the flexibility and deformability of the plunger, when pressure is applied in making an injection, the cocked plunger will allow a small amount of drug seepage proximally, thus reducing by a variable and uncontrolled amount the dose injected.

It is an object of our invention to provide a means for overcoming seepage due to cocking of a syringe plunger.

It is another object of our invention to provide a flexible connection between push rod and plunger which does not interfere with in-and out control of the plunger.

Other objects and advantages will be apparent from the following disclosure.

According to our invention we provide means in the distal end of the push rod for positive engagement with the syringe plunger, thus providing positive control of aspiration and injection, said means being attached to the push rod by a flexible web or elastic membrane or diaphragm, thus permitting a limited degree of axial embodiments of our invention are intended to be illustrative only and not to limit the scope of our invention which is defined in the appended claims.

In the drawing Fig. l is a partially sectioned side view of our invention applied to a disposable syringe nited States atent.

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showing how cocking of the plunger is avoided by our invention when the push rod is out of axial alinement;

Fig. 2 is a longitudinal section of one embodiment of our invention and Fig. 3 is a view of the distal end of the push rod shown in Fig. 2;

Fig. 4- is a longitudinal section of the distal end of a modification of the push rod shown in Fig. 2; and

Fig. 5 is a view of the distal end of the push rod shown in Fig. 4;

Fig. 6 illustrates a further modification of the distal end of the novel push rod;

Fig. 7 is a longitudinal section of a needle hub adapted to mate with the push rod shown in Fig. 2;

Fig. 8 illustrates a modified connection between push rod and needle hub; and

Figs. 9 and 10 illustrate modifications of the connection of the push rod with the plunger.

Our invention comprises essentially a tubular push rod 1 having a central bore 2. It is provided at its proximal end with means for fitting snugly over a needle hub 3 of an injection syringe permitting use of the push rod as a needle shield before injection. This means may be an internal thread 4 mating with an external thread 5 on the needle hub. Alternatively it may be a female taper 6 mating with a complementary male taper 13 on the needle hub (Figs. 2 and 7) or a series of internal circumferential ridges 18 in the bore of push rod 19 may provide a friction fit on the cylindrical portion 20 of a needle hub 21 (Fig. 8).

At its distal end the push rod is provided with a socket 7 adapted to matewith a threaded stud 8 fixed in plunger 9. This socket may be provided with an internal mating thread 10 as shown in Fig. 6, but we prefer to make the push rod of a material capable of self-threading, e. g. of synthetic plastic, in which case thread 10 may be omitted as shown in Figs. 2 and 4.

Socket 7 is mounted in bore 2 of push rod 1 at its distal end by means of a thin flexible integral web 11. This web may be a solid disc as shown in Figs. 2 and 3 or may be in the form of a wheel having spokes 12 connecting socket 7 with push rod 1 as shown in Figs. 4, 5 and 6. Socket 7 is mounted so as to extend somewhat beyond the distal end of the push rod in order to permit angular movement of the latter without distorting plunger 9 by abutment of the end of the push rod against the plunger. We have found that web 11, whether solid or spoked, can be made sufficiently thin to permit the required flexibility while retaining sufficient strength to withstand the pressure and tension required for injection and aspiration respectively. For example a solid web 11 made of a rigid polyethylene 0.012-0.0l5 inch thick is satisfactory in a push rod having a bore of 0.251 inch internal diameter with a socket 0.200 inch in external diameter; i. e. the web has a span of 0.025 inch. A. web made of four spokes 12 as shown in Fig. 5

inch thick is satisfactory with a span of 0.037 inch.

These dimensions are exemplary only. Other forms of web may, of course, be used with appropriate changes in dimensions, e. g. webs with 3 or 5 spokes or perforated webs. The web may be integral with the push rod or of a different material, e. g. a thin metal web molded into a plastic push rod.

In Fig. l the misalinement shown is approximately 10, and such misalinement is possible with our invention without serious cocking of p the plunger.

A needle hub suitable for use with the push rod of Fig. 2 is shown in longitudinal section and unassembled in Fig. 7. As noted above, male taper 13 mates with female taper 6 of rod 1. In assembled form skirt 14 is crimped around flanged distal opening of the syringe W a?) 15 and injection needle 16 is staked in bore 17 of the hub.

Fig. 9 illustrates a push rod 22 having an enlarged threaded stud 23 mating with internally threaded recess 24 in plunger 25. Stud 23 is connected to push rod 22 by flexible web 26. The depth of recess 24 is less than the length of stud 23, thus preventing web 26 from butting against plunger 25 and allowing push rod 22 to cant without cooking the plunger.

Fig. 10 illustrates a push rod 27 having a smooth stud 28 of selflthreading material adapted to mate with internally threaded metal socket 29 molded in plunger 34 As in the modification shown in Fig. 9 and for the same reason the depth of the recess in socket 29 is less than the length of stud 28.

In the specification and claims distal refers to a direction or position towards the needle end of the syringe and proximal refers to the opposite direction.

The word web is used to denote a thin disc-like portion connecting a socket or stud with the push rod as described, which web maybe continuous or perforated or constituted of spokes or the like.

We claim:

1. A tubular push rod having at its distal end means for positive engagement with the plunger of a syringe, and a flexible web connecting said means with the push rod.

2. A push rod as defined in claim 1 in which said engagement means comprises a socket adapted to make threaded engagement with a stud on the plunger.

53. A push rod as defined in claim 1 in which said engagement means comprises a stud adapted to make threaded engagement with a recess in the plunger.

4. In a push rod adapted for use in a disposable syringe, the rod having a central bore permitting its use as a needle shield prior to injection, having at its proximal end means for removably securing it to a syringe when serving as a needle shield and having at its distal end 4%. means for positive engagement with the syringe plunger when being used for injection, the improvement which comprises a flexible web connecting said engagement means with the bore of the push rod.

5. The improvement in a push rod as defined in claim 4 in which said engagement means comprises a socket adapted to make threaded engagement with a stud on the plunger.

6. The improvement in a push rod as defined in claim 4 in which said engagement means comprises a stud adapted to make threaded engagement with a recess in the plunger.

7. In combination with a disposable syringe comprising a body, a plunger provided with a threaded stud, a needle hub attached to the body, and an injection needle mounted in the needle hub: a tubular push rod provided at its distal end with a socket adapted to mate with the stud in the plunger, and a flexible web joining the socket with the bore of the push rod.

8. A combination as defined in claim 7 in which the socket is of self-threading material.

9. A combination as defined in claim 7 in which the socket is provided with an internal thread.

10. In combination with a disposable syringe comprising a body, a plunger provided with a threaded recess, a needle hub attached to the body and an injection needle mounted in the needle hub: a tubular push rod provided at its distal end with a stud adapted to mate with the recess in the plunger, and a flexible web joining the stud with the bore of the push rod.

References Cited in the file of this patent UNITED STATES PATENTS 

